Identification of RNA-based cell-type markers for stem-cell manufacturing systems with a statistical scoring function.

Cell-type biomarkers are useful in stem-cell manufacturing to monitor cell purity, quantity, and quality. However, the study on cell-type markers, specifically for stem cell manufacture, is limited. Emerging questions include which RNA transcripts can serve as biomarkers during stem cell culture and how to discover these biomarkers efficiently and precisely.

Electrochemical Beacon Method to Quantify 10 Attomolar Nucleic Acids with a Semilog Dynamic Range of 7 Orders of Magnitude.

Change in the dynamics of single-stranded DNA or RNA probes tethered to an Au electrode on immunospecific binding to the analyte is a versatile approach to quantify a variety of molecules, such as heavy metal ions, pesticides, proteins, and nucleic acids (NAs). A widely studied approach is the electrochemical beacon method where the redox of a dye attached to the probe decreases as its proximity to the underlying electrode changes on binding. The limit of quantification (LOQ) defined by the semilog dependence of the signal on target concentration is in the picomolar range.

Quantitative PCR of Small Nucleic Acids: Size Matters.

Quantitative dysregulation in small nucleic acids (NA), such as microRNA (miRNA), extracted from minimally invasive biopsies, such as, blood, stool, urine, nose, throat, are promising biomarker for diseases diagnosis and management. We quantify the effect of the extra step of poly(A) ligation for cDNA synthesis and small size of the NA on the limit of quantification (LOQ) of quantitative PCR (qPCR), the gold standard to measure copy number. It was discovered that for small NA, the cycle threshold, Ct that is proportional to -log[c], where [c] is the concentration of the target NA exhibits a sharp transition.

Electrochemical Deposition of Polyelectrolytes Is Maximum at the Potential of Zero Charge.

Electrochemical deposition of cationic and anionic polyelectrolyte on a Au electrode is studied as a function of applied potential between the electrode and the solution of monovalent electrolyte. The deposition is measured by open circuit potential relative to a pristine electrode in a reference solution (100 mM NaCl). The rate of deposition is measured by a home-built electrochemical-optical method in real time.

Electrochemical Characteristics of a DNA Modified Electrode as a Function of Percent Binding.

Electrochemical characteristics of immobilized double-stranded DNA (dsDNA) on a Au electrode were studied as a function of coverage using a home-built optoelectrochemical method. The method allows probing of local redox processes on a 6 μm spot by measuring both differential reflectivity (SEED-R) and interferometry (SEED-I). The former is sensitive to redox ions that tend to adsorb to the electrode, while SEED-I is sensitive to nonadsorbing ions.

Simultaneous Printing of Two Inks by Contact Lithography.

Microcontact printing (μCP) is a valuable technique used to fabricate complex patterns on surfaces for applications such as sensors, cell seeding, self-assembled monolayers of proteins and nanoparticles, and micromachining. The process is very precise but is typically confined to depositing a single type of ink per print, which limits the complexity of using multifunctionality patterns. Here we describe a process by which two inks are printed concomitantly in a single operation to create an alternating pattern of hydrophobic and hydrophilic characteristics.

Quantitative Electrochemical DNA Microarray on a Monolith Electrode with Ten Attomolar Sensitivity, 100% Specificity, and Zero Background.

Circulating microRNA are promising diagnostic and prognostic biomarkers of disease in quantitative blood tests. A label-free, PCR-free, electrochemical microarray technology on a monolith electrode is described, with 10 attomolar (aM) sensitivity and responsiveness to binding of <1 zeptomole of target to immobilized ssDNA probes with zero background. Specificity is 100% in a mixture with five nonspecific miRNA each with a 10-fold higher concentration.

Noninvasive Measurement of Electrical Events Associated with a Single Chlorovirus Infection of a Microalgal Cell.

Chlorovirus Paramecium bursaria chlorella virus 1 (PBCV-1) contains a viral-encoded K(+) channel imbedded in its internal membrane, which triggers host plasma membrane depolarization during virus infection. This early stage of infection was monitored at high resolution by recording the cell membrane depolarization of a single Chlorella cell during infection by a single PBCV-1 particle. The measurement was achieved by depositing the cells onto a network of one-dimensional necklaces of Au nanoparticles, which spanned two electrodes 70 μm apart.

Tactile imaging of an imbedded palpable structure for breast cancer screening.

Apart from texture, the human finger can sense palpation. The detection of an imbedded structure is a fine balance between the relative stiffness of the matrix, the object, and the device. If the device is too soft, its high responsiveness will limit the depth to which the imbedded structure can be detected.

Negative printing by soft lithography.

In inkless microcontact printing (IμCP) by soft lithography, the poly(dimethylsiloxane) (PDMS) stamp transfers uncured polymer to a substrate corresponding to its pattern. The spontaneous diffusion of PDMS oligomers to the surface of the stamp that gives rise to this deleterious side effect has been leveraged to fabricate a variety of devices, such as organic thin film transistors, single-electron devices, and biomolecular chips. Here we report an anomalous observation on a partially cured PDMS stamp where the transfer of oligomers onto Au occurred on regions that were not in contact with the stamp, while the surface in contact with the stamp was pristine with no polymer.

Multianalyte electrochemical biosensor on a monolith electrode by optically scanning the electrical double layer.

Redox on an electrode is an interfacial phenomenon that modulates the charge in the electrical double layer (EDL). A novel instrument, the Scanning Electrometer for Electrical Double-layer (SEED) has been developed to measure multiple enzyme reactions on a monolith electrode due to immunospecific binding with a mixture of respective analytes. SEED quantitatively maps the local redox reaction by scanning a laser on the array of enzyme monolayer spots immobilized on the monolith electrode.

Noninvasive measurement of membrane potential modulation in microorganisms: photosynthesis in green algae.

Cell membrane potential (CMP) modulation is a physical measurement to quantitatively probe cell physiology in real time at high specificity. Electrochemical field effect transistors (eFETs) made from graphene and Si nanowire provide strong mechanical and electrical coupling with neurons and muscle cells to noninvasively measure CMP at high sensitivity. To date, there are no noninvasive methods to study electrophysiology of microorganisms because of stiff cell walls and significantly smaller membrane polarizations.

Self-assembly of gold nanoparticles on poly(allylamine hydrochloride) nanofiber: a new route to fabricate "necklace" as single electron devices.

Fabrication of a percolating conductive device exhibiting "necklace-like morphology" is being reported utilizing a new route. This device was fabricated by exploiting the electrostatic self-assembly of citrate capped negatively charged Au nanoparticles (NPs) (60 nm diameter) over positively charged poly(allylamine hydrochloride) (PAH) fibrous scaffold and followed by synthesis of small Au NPs (∼10 nm) on the PAH surface. These 10 nm Au NPs were selectively synthesized over the PAH fiber surface using the surface catalyzed reduction of Au precursor (HAuCl4), leading to a continuous conducting network.

Imaging electroluminescence from individual nanoparticles in an array exhibiting room temperature single electron effect.

Electroluminescence (EL) from the monolayer of a network of a one-dimensional (1D) necklace of 10 nm Au particles (nano)cemented by CdS is imaged. The EL and photoluminescence (PL) spectra confirm the emission from CdS. The EL emission blinks and is highly specular.

Single electron transistor in aqueous media.

A gold nanoparticle necklace array spanning a ∼30-micrometer-wide channel shows a robust coulomb blockade effect at room temperature with a threshold of 1V in air. When this device is operated in the aqueous solution, a gain of ∼130 fold in conductance is obtained in electrochemical gating, significantly higher than other nanomaterial-based electrochemical transistors.

Direct mapping of local redox current density on a monolith electrode by laser scanning.

An optical method of mapping local redox reaction over a monolith electrode using simple laser scanning is described. As the optical signal is linearly proportional to the maximum redox current that is measured concomitantly by voltammetry, the optical signal quantitatively maps the local redox current density distribution. The method is demonstrated on two types of reactions: (1) a reversible reaction where the redox moieties are ionic, and (2) an irreversible reaction on two different types of enzymes immobilized on the electrode where the reaction moieties are nonionic.

Ultrasoft 100 nm thick zero Poisson's ratio film with 60% reversible compressibility.

About a 100 nm thick multilayer film of nanoparticle monolayers and polymer layers is shown to behave like cellular-foam with a modulus below 100 KPa. The 1.25 cm radius film adhered to a rigid surface can be compressed reversibly to 60% strain.

Tuning the energy level offset between donor and acceptor with ferroelectric dipole layers for increased efficiency in bilayer organic photovoltaic cells.

Ultrathin ferroelectric polyvinylidene fluoride (70%)-tetrafluoroethylene (30%) copolymer film is inserted between the poly3(hexylthiophene) (P3HT) donor and [6,6]-phenyl-C61-butyric acid methylester (PCBM) acceptor layers as the dipole layer to tune the relative energy levels, which can potentially maximize the open circuit voltage of bilayer organic solar cells. In this work, the power conversion efficiency of P3HT/PCBM bilayer solar cells is demonstrated to be doubled with the inserted dipoles.

Modulation of electron tunneling in a nanoparticle array by sound waves: an avenue to high-speed, high-sensitivity sensors.

Using an electrostatic self-assembly process, metal nanoparticles are deposited on polyelectrolyte fibers such that the interparticle distance between the nanoparticles is comparable to the polyelectrolyte's molecular width. By modulating the dielectric properties of the interparticle polymer layer, a highly sensitive, reversible humidity sensor with an ultrafast response time of ≈3 ms is demonstrated. The higher sensitivity at low humidity shows a conductivity increase by over two orders of magnitude in response to a change in relative humidity from 21 to 1%.

Self-assembled nanoparticle necklaces network showing single-electron switching at room temperature and biogating current by living microorganisms.

A network of one-dimensional (1D) Au nanoparticle necklaces is synthesized and shown to exhibit electronic switching, that is, gating, by the metabolic activity of yeast cells deposited on the structure. Without the cells, the network exhibits the Coulomb blockade effect at room temperature with a sharp threshold voltage, V(T) of approximately 0.45 V, which corresponds to a switching energy of approximately 20 kT.

Ion mediated monolayer deposition of gold nanoparticles on microorganisms: discrimination by age.

A general strategy to target cells by nanoparticles for drug delivery, imaging, or diagnostics involves immunospecific binding between the probes and target molecules on the particles and on the cell surface, respectively. Usually, the macromolecular nature of the molecules requires a specific conformation to achieve the desired immunospecificity, and the extent of deposition of particles is limited by the number of receptor molecules present on the cell. In this report, we successfully obtain targeted binding by decorating the nanoparticle with simple ions, such as Ca(2+), without affecting the cell's vitality.

Localized electrochemistry on a 10 microm spot on a monolith large electrode: an avenue for electrochemical microarray analysis.

By measurement of the modulation of ions under an ac field at the electrode/electrolyte interface layer (EIL) at a spatial modulation of 0.0001 nm, a quantitative measurement of local redox current on a 10 microm spot of a working electrode is achieved at a sensitivity of 0.02 nA/spot.

Tactile devices to sense touch on a par with a human finger.

Our sense of touch enables us to recognize texture and shape and to grasp objects. The challenge in making an electronic skin which can emulate touch for applications such as a humanoid robot or minimally invasive and remote surgery is both in mimicking the (passive) mechanical properties of the dermis and the characteristics of the sensing mechanism, especially the intrinsic digital nature of neurons. Significant progress has been made towards developing an electronic skin by using a variety of materials and physical concepts, but the challenge of emulating the sense of touch remains.

Polyelectrolyte mediated scalable synthesis of highly stable silver nanocubes in less than a minute using microwave irradiation.

Silver nanocubes were synthesized for the first time in large quantities on gold seed in the presence of a polyelectrolyte using microwave heating for 60-120 s. Our experiment indicates that the polyelectrolyte directs the growth of the particle in a specified crystallographic direction resulting in the faceted particle, i.e.